1. Field of the Invention
The present invention relates to a floating cover for a liquid storage tank, and more particularly, to a liquid surface contact internal floating cover constructed with a plurality of floating panels, and a process for monitoring leaks within each of the floating panels.
2. Description of the Background Art
Floating covers have previously been used inside cylindrical liquid storage tanks to ride vertically along the cylindrical wall of the tanks between the roof and bottom as the volume of fluid held by the tank varies. Typically, the floating cover floats above the liquid and moves up and down depending on the amount of the liquid. A plurality of buoyant panels or honeycomb type pans are assembled to form the floating cover. This conventional floating cover, however, is expensive to manufacture and erect inside the frame of the tank. Accordingly, periodic inspection and maintenance of the cover is desirable in order to obtain the full life of the cover.
The current design for full surface contact floating covers uses honeycomb panels that are manufactured by bonding an aluminum channel frame to the honeycomb panel. The honeycomb panel may have all sealed cells or all interconnected cells. If some of the cells of an individually sealed honeycomb are opened to invasion of the product held by the tank, there is currently no way of detecting the invasion except by observation of the escaped product as it drips out of the panel after the tank has been taken out of service and emptied. The trapped liquid will, however, slowly drip out of the panel and present a grave safety hazard to the maintenance people working within the interior of the tank. If a cell of an interconnecting cell type of honeycomb panel is violated, then all cells are violated, making it almost impossible to find the original leaking cell. The whole panel must be replaced.
The owners and managers of tanks must periodically inspect the interior of the tank and make repairs. This entails a removal of the contents of the tank, a purging of gaseous phase vapors from the interior of the tank, an introduction of ambient atmospheric air into the interior of the tank, and continuous or at least intermittent monitoring of the atmosphere within the interior of the tank. The owner of the tank needs assurance that, before personnel enter the interior of the empty tank, and while work (particularly using arc or open flame torches) is performed within the interior of the tank, the tank has been completely emptied and cleaned, and is safe for both the personnel and the type of work being performed. This assurance requires that there be no remaining hazardous pockets of the contents of the tank within the floating roof.
Currently, contemporary designers of buoyant panels provide no convenient technique for detecting the presence of moisture and condensate within individual buoyant panels.